Xerographic copying machines are well known and widespread in use. A typical component in such system is a toner cartridge for containing and dispensing the toner utilized in reproduction.
A primary objective of many toner dispensing systems is to meter toner out of the cartridge and into the developer at a controlled rate; so as to match (over the long term) the rate at which toner is used by the copying process. This method of toner addition has to be adjusted to match the rate of toner depletion which is very dependent on the type of copies (the average percent coverage) being made. While this may be achievable over a long term average, there are variations in the originals and in the percent coverage that cause the toner concentration to vary to an unacceptable degree.
Sophisticated control systems have however become available and with the lower costs of sensing the actual toner concentration they provide the opportunity to close the feedback loop on a relatively short time scale. In this regard, under the conditions of closed-loop, the toner is added in response to low toner concentration, and not because some predetermined time interval has passed. Variations in the area of coverage of the originals are promptly met with the appropriate action of toner dispenser. The major time constant in the system response now becomes the total volume developer in the sump and the sensitivity of the toner concentration sensor. The control system is designed in view of these two parameters, and the total system latitude for toner concentration.
A system with active, closed-loop control, lessens the requirements often put on the toner cartridge: that of dispensing the same amount of toner throughout the life of the cartridge. The variation in toner quantity from a ne cartridge to a nearly spent cartridge has a marked effect on the quantity dispensed, particularly in gravity dispensing schemes.
With a closed-loop control, it allows such a requirement to be reduced to such an extent that the cartridge need only dispense toner evenly across the process width. Further, it does not matter what actual quantity is dispensed as long as the amount is sufficient in view of the closed loop sample time and latitude of the development system as a whole.
While some existing toner cartridges utilize active mechanisms to dispense, other toner addition schemes use gravity to cause the toner to exit the cartridge and replenish the developer. An example of toner cartridge of the latter type can be seen in U.S. Pat. No. 3,722,471 issued Mar. 27, 1973 to Stoffel. This invention discloses the use of a cartridge which is cylindrical and adapted to rotate over a developer reservoir so as to provide a metered amount of toner at a prescribed rate. A series of chutes are provided, communicating with an opening in the cartridge wall to allow for the separating an amount of toner and allowing it to be dispensed therefrom. The dispenser is meant to dispense an amount of toner into the developer reservoir in proportion to the amount of toner consumed. While such a gravity feed cartridge may be acceptable in the device envisioned therein, there exists a need for a more accurate one and one in which its operation is not adversely affected as the cartridge goes from its full to empty condition.
With the foregoing in mind, there exists a need for a copying machine toner cartridge which is relatively simple in structure and operation, but yet is effective in dispensing toner in an efficient and controlled fashion